When ROBIN THICKE sued MARVIN GAYE'S family . . . as a preemptive strike to a possible copyright infringement showdown . . . he seemed sure "Blurred Lines" was NOT a rip-off of Marvin's "Got to Give It Up".

But maybe Robin DID recognize that he could be in trouble . . . because he supposedly offered the family a "six-figure settlement" BEFORE he sued them. They turned him down, and that's when he went ahead with his lawsuit.

No one has commented on this report . . . but Marvin's son has told TMZ, quote, "We're not happy with the way that he went about doing business, let alone suing us for something where he clearly got his inspiration from at the least."

Earlier this year, Robin had this to say about "Blurred Lines" in an interview with "GQ" magazine: Quote, "PHARRELL and I were in the studio and I told him that one of my favorite songs of all time was Marvin Gaye's 'Got to Give It Up'.

"I was like, 'Damn, we should make something like that, something with that groove.' Then he started playing a little something and we literally wrote the song in about a half hour and recorded it. The whole thing was done in a couple hours."